Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Qual é a média de Mark Grieb quando seus TDs são menores que 2?
 ###Tabelas: CREATE TABLE running_backs (running_backs_id AUTO_INCREMENT PRIMARY KEY, Player VARCHAR, Car. INT, Yards INT, Avg. INT, TD's INT, Long INT) CREATE TABLE seasonal_timeslots_ratings (seasonal_timeslots_ratings_id AUTO_INCREMENT PRIMARY KEY, Season INT, TV season VARCHAR, Regular Timeslot (EDT) VARCHAR, Episode count INT, Season premiere VARCHAR, Season finale VARCHAR, Rank VARCHAR, Rating VARCHAR) CREATE TABLE summary_of_qualification (summary_of_qualification_id AUTO_INCREMENT PRIMARY KEY, Confederation VARCHAR, Teams started VARCHAR, Teams that have secured qualification VARCHAR, Teams that can still qualify VARCHAR, Teams that have been eliminated VARCHAR, Remaining places in finals VARCHAR, Total places in finals VARCHAR, Qualifying start date VARCHAR, Qualifying end date VARCHAR) CREATE TABLE missed_opportunities (missed_opportunities_id AUTO_INCREMENT PRIMARY KEY, Player VARCHAR, Team VARCHAR, Opponent VARCHAR, Year INT, Score VARCHAR, Outcome VARCHAR) CREATE TABLE current_destinations (current_destinations_id AUTO_INCREMENT PRIMARY KEY, City VARCHAR, Country VARCHAR, IATA VARCHAR, ICAO VARCHAR, Airport VARCHAR)  
SELECT SUM Avg. FROM running_backs WHERE Player = mark grieb AND TD's < 2